Reaktionstakt

Reaktionstakt, or reaction rate, is the speed at which chemical change occurs in a system. It is commonly defined as the change in concentration of a reactant or product with respect to time, for example the disappearance of A or the formation of B. In closed solutions the rate is typically expressed in moles per liter per second (mol L-1 s-1), while gas-phase reactions may be described by changes in pressure.

A rate law expresses how the rate depends on concentrations and temperature. For a reaction A + B → products, the rate often follows rate = k [A]^m [B]^n, where m and n are reaction orders. The overall order is m+n. The rate constant k increases with temperature and is described by the Arrhenius equation, k = A exp(-Ea/RT).

Several factors influence the rate: reactant concentrations, temperature, catalysts, surface area for heterogeneous reactions, solvent effects, and mixing. In heterogeneous catalysis, the rate is controlled by surface processes and the rate-determining step. Pressure matters for gas reactions, and stirrer speed can affect mass transfer.

Experimentally, rates are determined by initial-rate methods or by monitoring concentration over time and using integrated rate laws. Depending on the mechanism, reactions may be zero-, first-, or second-order with respect to a given species. Understanding kinetics helps in reactor design, safety analysis, and control of chemical processes.